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Many that pay close attention to the climate debate are aware that there are different choices of instrumental data to choose from. The ones that show lower temperatures get used by skeptics and the ones that show higher temperatures get used by warmists. This is a form of cherry picking. The person choosing the data gets to pick which one they use. In this way they feel they can make the stronger case.

Considering that there is a non-trivial difference between the sets of data I feel that this problem needs a solution. Since there is no standard, I decided to make one that I will use myself and make it available to anyone that wants to use it as well. Here are the four different sources I use for my merged or blended set. They are comprised of two station sets and the two satellite sets.

CRU – The original global set. It covers from 1850-current. It is a station set.

Hadley – A different global set that also covers from 1850-current. Also a station set.

UAH – This is a satellite measurement of wavelength. It has only been around since 1979, but covers most of the Earth instead of just stations.

RSS – Also a satellite measurement of wavelength. Also around since 1979, but covers less of the Earth, it especially misses portions around the poles, especially in the Antarctic region.

The Four Global Temperature Sets

The station data goes back to 1850. These sets of data are constructed by taking the high and the low temperature of the stations around the planet and averaging the temperatures until the annual average temperature anomaly is reached. It is less accurate as many factors can impact the results. One of the biggest limitations is that the temperature can only be measured where there is a thermometer hooked up. The rest of the area is essentially guessed. Many portions of the Earth do not have stations and this greatly limits the station data.

Satellite data is not direct measurement of temperature, but since each satellite is measuring each spot of the Earth the same error would apply to the whole measurement. Since they cover most of the Earth directly they measure much more of the Earth’s surface. For these reasons they are considered to be more accurate. The big limiting factor is the data only goes back to 1979. I think most people would agree that having 160 years of satellite data would be very helpful in the debate.

I am frustrated by the limitation of the available data. So I decided to use the above 4 measurements to create a single temperature record. From 1850-1978 it uses a simple average of the CRU and Hadley data. From 1979 it weights the two satellites equally with 33% and then the station average gets a 33% weight. One fortunate event was that there was not much of a difference between the 4 sets in 1979. That the methods have diverged since then is the reason why picking one set is a form of cherry picking. Warmists like the station data and skeptics like the satellite data.

The Merged Global Set

Merged Set - Past 40 Years

The weighting options are pretty clear in the excel chart. Changing a single cell will change the weighting for all everything. I used the older version so more people will be able to open it without problem. If many people request the data to be in csv form I will also add that as a download option.

While I know that this is not a pure scientific method, it is a great engineering method for using as much of the information as possible. There is little chance it will be more inaccurate in the long run and any problems with one set will be lessened by the inclusion of the others. I will also make this available for anyone to use. I will update it each month as soon as I have all the data.

There is also a 9 year moving average that is also charted. I would rather use a standard set that includes as much information as possible and includes more than a single source. I hope that more people will start using this or one similar to it. A lot of work goes into these data sets and while none of them is perfect, hopefully the merged set will be helpful to everyone.

Finally. I am not happy with the name, if you have a better one, please let me know. I have been switching between merged and blended, but I don’t really like either of them.

Posted in Anomaly by inconvenientskeptic on October 10th, 2010 at 9:27 pm.

This post has 4 comments

I have 2 problems with this data.
1. Both groups tend to treat the data as totally accurate without weighting the data based on it’s adherence to standards(last calibrated(satellites not available for physical calibration), effects of location(on a black roof or on tarmac used by jets,etc), accuracy(electronic(tenth of degree), mercury filled tube(2 degrees), etc.)).
2. Graphs will use an unrealistic graduation as the temperature may only be accurate to 1 degree yet the chart uses .1 degree increments.

Keep it real, satellites hundreds of miles up can be off more than 100 degrees(pointed out by many skeptics who show surface data of 400 degrees). Stations are run by people, which always introduces some degree of error.
I believe if the data was displayed with a reasonable margin for error then the charts would be displaying single degree changes which would prove inconclusive. This is truly the state of climate research as the current references cannot be trusted to be accurate at a tenth of degree.

I fully agree that for absolute measurements there are problems. However this is where using the anomaly is a significant benefit. If the same thermometer is off on calibration, but is accurate relative to itself, the long term anomaly will still be accurate.

In addition using the anomaly allows each source of data to only contribute the relative changes in temperature. This included the satellite data.

The satellite’s do not directly measure temperature. They are accurate enough that weather forecasts are now reasonably accurate for up to a week. Again, anomaly for them is still internally relative so using the anomaly allows multiple sources to be compared.

The relative change over the past 40 years indicates that the Earth has warmed, with the past 10 years being the warmest. I do not dispute this. How significant this is and what it means is where I become a skeptic.

I would like there to be a standard temperature that everyone agrees to use.